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Overcoming Charge Collection Limitation at Solid/Liquid Interface by a Controllable Crystal Deficient Overlayer
Author(s) -
Zhang Kan,
Ravishankar Sandheep,
Ma Ming,
Veerappan Ganapathy,
Bisquert Juan,
FabregatSantiago Francisco,
Park Jong Hyeok
Publication year - 2017
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201600923
Subject(s) - materials science , overlayer , photocurrent , crystal (programming language) , amorphous solid , water splitting , optoelectronics , nanowire , energy conversion efficiency , analytical chemistry (journal) , photocatalysis , crystallography , condensed matter physics , chemistry , physics , biochemistry , chromatography , computer science , programming language , catalysis
Bulk and surface charge recombination of photoelectrode are two key processes that significantly hinder solar‐to‐fuel conversion of photoelectrochemical cell (PEC). In this study, the function of a “crystal‐deficient” overlayer is unveiled, which outperforms a traditionally used amorphous or crystalline overlayer in PEC water splitting by exhibiting a high conductivity and large electron diffusion length to enable unlimited electron collection. The optimized ≈2.5 nm thickness of the “crystal‐deficient” shell results in a depletion layer with a width of 3 nm, which overcomes the flat band limitation of the photovoltage and increases the light absorptivity in the wavelength range from 300 to 420 nm. In addition, a 50‐fold increase in the conductivity yields a one‐order‐of‐magnitude increase in the diffusion length of an electron ( L n )(≈20 μm), allowing for unlimited electron collection in the 1.9 μm TiO 2 nanowire array with the “crystal‐deficient” shell. The controllable “crystal‐deficient” overlayer in rutile TiO 2 nanowires photoanode achieves a photocurrent density greater than 2.0 mA cm −2 at 1.23 V versus reversible hydrogen electrode (RHE), a 1.18% applied bias photon‐to‐current efficiency at 0.49 V versus RHE, a faradaic efficiency greater than 93.5% at 0.6 V versus Pt under air mass 1.5G simulated solar light illumination (100 mW cm −2 ).